In the application of tire repair patches to the surface of tires and especially large truck and off the road vehicle tires uncured patches are preferred because they have the greatest adhesion to the tires. The uncured patch is heated with the tire in an autoclave or mold which requires a substantial amount of energy in the form of heat applied over a significant number of hours. Not only is the energy requirement high but the heating time is added to the heat history of the tire and reduces the number of times the tire can be retreaded.
An extended heating time is required because the heat must be transmitted to the reinforcing plies through the cushion gum layers surrounding the plies. Also on the tire wall side of the patch the heat must be transmitted through the tire wall as well as the cushion gum layer.
When a tire has needed repair and retreading it has been the practice to insert a plug core in the injury, apply the uncured patch and then put the tire in an autoclave for curing the patch and plug at elevated temperatures for about 8 to 10 hours. After this the tire has been buffed and placed in a retread mold for about 12 to 18 hours to cure the new tread at elevated temperatures and pressures. It has not been possible to cure the plug core and uncured patch during the retreading operation because the patch does not have sufficient strength to bridge the injury and is deformed into the plug.
In an effort to save time the tire has been repaired by inserting a plug core in the tire wall injury and then spot curing that part of the tire. A chemical patch has then been applied and is adhered to the tire wall during the retreading operation. Although there is a time saving the adhesion obtainable with this method is substantially less than that provided by an uncured patch. The cost of the chemical cure patch is also greater than the cost of an uncured patch.